Labels have been conventionally fixed onto an article with pressure sensitive adhesives in the case of thermoplastic films (such as polyolefins, e.g. biaxially oriented polypropylene-BOPP) and an adhesive dispersed in an aqueous medium in the case of paper. The latter are often referred to as wet glue labels but can also be called cold glue or just glue labels.
The market for alcoholic beverages such as beer, wine or spirits is more and more competitive and breweries need to find ways of capturing their audience and enticing them to purchase their product. Packaging is a major part of the promotional mix especially at point of sale in supermarkets and the drive for differentiation amongst the manufacturers is furious.
The ‘no-label’ look came into fashion in the pressure sensitive (PS) market several years ago and retailers have found many advantages from this new form of shelf appeal. This is achieved by applying a clear transparent label to the article (or a coloured transparent label matched to the colour of the article). As an alternative or as well a transparent or clear label can be coated (e.g. printed or metallised) completely or partially on its reverse side (i.e. the “interior” side to be adhered to the article) so that such a coat or printing is better protected from wear and tear (rubbing, attack by solvents etc) as it is not on the exterior of the article.
However due to the process used to apply a wet glue label, the conventional transparent plastic films (OPP, polyester-PE, polyethylene phthalate-PET) currently used in the PS market have various disadvantages when used as the substrate to produce a transparent wet glue label. The properties of these thermoplastic films are different from the paper labels used on conventional wet glue machines. For example thermoplastic films have a high barrier to moisture (they are not semi-permeable to water) and this causes a wet glue to take much longer to dry (and hence the label to fix in place) which can be disadvantageous on a high speed labelling line or where precise location of the label is required. Thus thermoplastic films are not an ideal replacement for a paper label on a conventional production line set up to apply a wet glue label to an article such as a bottle. Aqueous coatings are also not easily compatible with and do not adhere well to such thermoplastic films which are often hydrophobic without further surface treatments.
The substrate conventionally used to prepare wet glue labels is paper which is not transparent. Thermoplastic films are transparent but because of the previous stated disadvantages with thermoplastic films and wet glue coatings, it has been necessary to use pressure sensitive adhesives to provide an article with a no look label having acceptable performance. Thus manufactures currently using labelling equipment for paper wet glue labels are faced with a significant capital outlay and disruption to change the to equipment compatible with pressure sensitive labels if they wish to move to no-look labelling.
Certain water based adhesive systems have been developed for use with labels.
WO 97/00298 (Henkel) discloses an adhesive system for gluing all-around plastic labels onto plastic bodies. The adhesive system has a pick-up glue and an overlapping glue. It is characterised in that the pick-up glue has a sufficient wet gluing power in the wet state and does not adhere to at least one of the substrates in the dried state. The pick-up glue contains 5 to 85% by weight of at least one water-soluble polymer based on casein, starch, dextrin, glucose, polyvinyl alcohol, polyurethane or polyacrylic acid, 0 to 1.0% by weight of at least one anti-foaming agent, and 0 to 1.0% by weight of at least one preservative, the remaining percentage being water.
U.S. Pat. Nos. 4,464,202 and 4,462,838 (both Henkel) describes an aqueous adhesive compositions useful for labeling bottles More particularly, these inventions relate to aqueous adhesive compositions for mechanical labeling based upon starch derivatives and having a content of flow-regulating additives and, optionally, other customary additives such as: (a) at least one hydroxyalkyl ether of oxidized starch with a mean degree of substitution (MS) of 0.2, together with (b) at least one polymer dissolved in the aqueous phase, the polymer being selected from the group consisting of water-soluble cellulose derivatives, water-soluble synthetic polymers, casein, and water-soluble starch derivatives different from component (a).
U.S. Pat. No. 4,675,351 (Borden Inc.) describes an adhesive formulation useful for applying a paper label to a glass bottle, having the tack and rheology making it suitable for use in modern labeling equipment, and imparting water immersion resistance in ice water for a period of at least 72 hours, which, it based on soy protein isolate and does not use casein.
U.S. Pat. No. 5,455,066 (Henkel) describes a water-containing adhesive useful for labelling bottles. The adhesive is based on casein, water-soluble extenders, natural or synthetic resin acids, resin alcohols or resin esters, and an alcohol.
Other non-aqueous adhesives systems have been developed for use with polymer labels.
U.S. Pat. No. 5,366,251 (Brandt) describes a clear acrylic coated label which is used to provide a reverse side printed water-proof label. A heat activated solvent based adhesive system is used to bind the film to the article such as a glass container.